A bonding pad acts as a terminal for interconnecting a semiconductor device and a package. That is, following packaging of a pad, which exposes a predetermined portion of a metal line of an uppermost layer of the semiconductor device, connection is made to a region used for connection to a pin. Through such a bonding process, the semiconductor device is electrically connected to an external device such as a power supply assembly.
So that good bonding is realized, no foreign substances may be present nor can an oxidation layer be formed on a surface of a metal thin layer that forms the bonding pad. However, in conventional devices, the surface of the metal line becomes oxidized or a refractory metal is left remaining thereon. In either of these two cases, bonding is not performed in a satisfactory manner, a bonding line becomes unaligned, and other similar problems may occur.
If copper is used for the metal line, the copper may be easily corroded or oxidized thereby preventing bonding from being fully performed when the copper line is exposed to air. Even with the advantages of copper, particularly its ability to increase the driving speed of the device as a result of its low resistance, copper cannot typically be used for the uppermost metal line because of this drawback. In a case where copper is used despite this problem, a high bonding defect rate often results.